[PATCH v6 6/7] reboot: use devm_blocking_notifier_chain_register()

[Eliav Farber <farbere@amazon.com>]

Replace the manual devres_alloc() + register_reboot_notifier() pattern
with a single call to devm_blocking_notifier_chain_register(), removing
the devm_unregister_reboot_notifier() callback.

The removed callback wrapped unregister_reboot_notifier() in WARN_ON().
The generic helper ignores the unregister return value, so that warning
is gone. It could only fire if a caller had already unregistered the
notifier itself, which no in-tree user does.

Signed-off-by: Eliav Farber <farbere@amazon.com>
---
Changes in v6:
- Rebased onto v7.4-rc1.
- Commit message: record that the removed callback's WARN_ON() on a
  failed unregister goes away, because
  devm_blocking_notifier_chain_register() ignores the unregister return
  value. No change to the code.

Changes in v3:
- Fix commit message to accurately describe the old code as using
  devres_alloc() + register_reboot_notifier() (Sashiko)

 kernel/reboot.c | 24 ++----------------------
 1 file changed, 2 insertions(+), 22 deletions(-)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index 9a84401adde5..2fb8700c726d 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -146,30 +146,10 @@ int unregister_reboot_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL(unregister_reboot_notifier);
 
-static void devm_unregister_reboot_notifier(struct device *dev, void *res)
-{
-	WARN_ON(unregister_reboot_notifier(*(struct notifier_block **)res));
-}
-
 int devm_register_reboot_notifier(struct device *dev, struct notifier_block *nb)
 {
-	struct notifier_block **rcnb;
-	int ret;
-
-	rcnb = devres_alloc(devm_unregister_reboot_notifier,
-			    sizeof(*rcnb), GFP_KERNEL);
-	if (!rcnb)
-		return -ENOMEM;
-
-	ret = register_reboot_notifier(nb);
-	if (!ret) {
-		*rcnb = nb;
-		devres_add(dev, rcnb);
-	} else {
-		devres_free(rcnb);
-	}
-
-	return ret;
+	return devm_blocking_notifier_chain_register(dev,
+						     &reboot_notifier_list, nb);
 }
 EXPORT_SYMBOL(devm_register_reboot_notifier);
 
-- 
2.47.3